Man has used organic materials such as manure as fertilizers for years. More recently these organic materials have been pretreated in one fashion or other to create better nutrient balanced, less odoriferous fertilizer compositions.
For example, U.S. Pat. No. 4,743,287 to Robinson (May 10, 1988) discloses a humic acid fertilizer and method of making it. Robinson's method involves the use of a sealed reactor system, wherein organic material, water, and certain inorganic elements are mixed with, for example, an acid, to accomplish hydrolysis and a drastic change in pH, raising both the mix temperature and pressure. The mix is then subsequently mixed with a base, to provide a further temperature and pressure increase. The inorganic elements are added initially so that they may be available for humic acid bonding to the hydrolyzed organic molecules.
As can be determined by scrutinizing Robinson's process, the organic material is dried and composted resulting in a relatively expensive, time-consuming process. Also in Robinson's process, relatively high concentrations of sulfuric acid are used to achieve hydrolysis. For example, EXAMPLE I of Robinson indicates the use of an 8% sulfur content which works out to be 160 pounds (73 kg) of sulfur per acre if one acre is treated with one ton (909 kg) of humic acid fertilizer. This amount of sulfur can become significant if the fertilizer is repeatedly applied on an annual basis. Robinson also reports a maximum of 30% water content in his process which takes place in a closed vessel to prevent the loss of ammonia vapors.
Later work attributed to Robinson is described in European Patent publication numbers 428,014 A2,428,014 A3,428,015 A2, and 428,015 A3, published on May 22, 1991.